linux-ext4 - Re: [PATCH] jbd2: set freed flag while revoking a buffer which belongs to older transaction

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Message-ID: <20190112073957.GE2713@desktop>
Date:   Sat, 12 Jan 2019 15:39:57 +0800
From:   Eryu Guan <guaneryu@...il.com>
To:     "zhangyi (F)" <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, miaoxie@...wei.com
Subject: Re: [PATCH] jbd2: set freed flag while revoking a buffer which
 belongs to older transaction

On Thu, Jan 10, 2019 at 02:12:02PM +0800, zhangyi (F) wrote:
> Now, we capture a data corruption problem on ext4 while we're truncating
> an extent index block. Imaging that if we are revoking a buffer which
> has been journaled by the committing transaction, the buffer's jbddirty
> flag will not be cleared in jbd2_journal_forget(), so the commit code
> will set the buffer dirty flag again after refile the buffer.
> 
> fsx                               kjournald2
>                                   jbd2_journal_commit_transaction
> jbd2_journal_revoke                commit phase 1~5...
>  jbd2_journal_forget
>    belongs to older transaction    commit phase 6
>    jbddirty not clear               __jbd2_journal_refile_buffer
>                                      __jbd2_journal_unfile_buffer
>                                       test_clear_buffer_jbddirty
>                                        mark_buffer_dirty
> 
> Finally, if the freed extent index block was allocated again as data
> block by some other files, it may corrupt the file data when writing
> cached pages later, such as during umount time.
> 
> This patch mark buffer as freed when it already belongs to the
> committing transaction in jbd2_journal_forget(), so that commit code
> knows it should clear dirty bits when it is done with the buffer.
> 
> This problem can be reproduced by xfstests generic/455 easily with
> seeds (3246 3247 3248 3249).

Would you please capture the fsx ops sequences that could reproduce the
problem and replay it in a targeted regression test, like what
generic/{499,511} do? Thanks!

Eryu